(2) Principle of color matching with tristimulus values
According to the CIE standard colorimetry system, any natural color can be represented by spectral tristimulus values ​​X, Y, Z. At present, most advanced colorimetric instruments use this colorimetric system, ie the color of any object can be represented by the tristimulus values ​​X10, Y10, Z10. The principle of computer color matching is to use the principle of metamerism, that is, if the tristimulus values ​​X10, Y10, and Z10 of the two color samples are equal, the two are the same color.
A chromatogram-created look-up table describes the relationship between tristimulus values ​​and the percentage of each color ink dot. Let a color sample be overprinted by three types of inks a, b, and c. The dot percentages of the three inks are l, m, and n. The ratio of inks a, b, and c is l:m:n, and white ink. Take (1-l)+(1-m)+(1-n). This color matching system uses CIE standard light source D65 and 10° field of view data for calculation, while using CIELAB color difference formula: ΔEab=[(ΔL)2+(Δa)2 +(Δb)2]1/2 to calculate the standard color The color difference between the sample and the color matching sample.
We can see that using computer color matching with the tristimulus value can make the color of the color sample to be matched with a specific light source expressed by data. There is a corresponding relationship between the tristimulus value of the color sample and the ink ratio, and the color difference can be used. Check to see if the recipe meets the requirements.
(3) Three stimulus color matching methods
The tristimulus value of each color patch of the chromatogram and the percentage of dots of each ink were input into the computer to establish a basic database. In color matching, the tristimulus value of the target color sample is input into the system, the system calculates the mixed ink and its proportion, and outputs the formula prediction result. When the ink color matching result is dry, the tristimulus value is measured again, and the computer calculates the difference in color according to the color difference formula, and further correction instructions are made to promptly formulate the high-quality homochromatic color.
In terms of the quality requirements of color reproduction, according to the national standards for the clear requirements of the color difference ΔE*ab of the same batch of color decorating prints, this paper selects ΔE*ab≤3.
Chromatography includes most of the common colors. For the colors in the chromatogram, you can directly find the ratio of the ink, not the color in the chromatogram. You can first find the color with the smallest color difference in the chromatogram, and then use linear interpolation. Solution.
3. Computer color matching system
(1) Function of color matching system
The computer color matching system is a modern device that integrates a colorimeter, a computer, and a color matching software system. The basic role of computer color matching is to pre-store the color data of the ink used in color matching in a computer, and then calculate the mixing ratio of the color of the sample draft with these inks in order to achieve the purpose of the predetermined formula.
(2) The composition of the color matching system
1 hardware part of computer color matching system
Computer: Use Windows operating system, hard disk storage space at least 20MB; Spectrodensitometer; Chromatography.
2 computer color matching software system
The software main menu: displays the program directories in the color matching system software, so that the operator has a general understanding of the color matching software, so that the operator selects and invokes the programs displayed in the directory according to his own purpose.
Basic data files: Use Microsoft's Access to create database files, including two-color overprinting, three-color overprinting, and spot color overprinting. The document includes the establishment, management, data processing part and recipe storage program of the basic data file.
3 Formula calculation and correction
Call this program to calculate the color difference between the color match sample and the standard sample, select the recipe based on the color difference, and correct the recipe.
The color matching system software has a strong human-machine dialogue function. The operator can input the corresponding parameters and data according to the prompt on the computer screen to obtain the required ink formulation.
Color matching is a complex technical project involving light color theory, ink, paper, process, etc. The use of chromatography to perform tristimulus color matching overcomes the limitations of KM theory and is suitable for the characteristics of the printing industry, reducing the burden on the color matching staff. , Improve the color quality of the product, color matching speed, accuracy, and increase economic efficiency. Although there are still many places to be improved, such as different color differences calculated by the tristimulus value matching under different light sources, the color matching accuracy has a great relationship with the accuracy of the chromatogram. However, with the constant updating of computers, the more sophisticated instruments, the constant emergence of various mathematical methods, and the gradual standardization and dataization of materials, computer color matching will inevitably show unparalleled superiority.
Source: "Printing Technology"
According to the CIE standard colorimetry system, any natural color can be represented by spectral tristimulus values ​​X, Y, Z. At present, most advanced colorimetric instruments use this colorimetric system, ie the color of any object can be represented by the tristimulus values ​​X10, Y10, Z10. The principle of computer color matching is to use the principle of metamerism, that is, if the tristimulus values ​​X10, Y10, and Z10 of the two color samples are equal, the two are the same color.
A chromatogram-created look-up table describes the relationship between tristimulus values ​​and the percentage of each color ink dot. Let a color sample be overprinted by three types of inks a, b, and c. The dot percentages of the three inks are l, m, and n. The ratio of inks a, b, and c is l:m:n, and white ink. Take (1-l)+(1-m)+(1-n). This color matching system uses CIE standard light source D65 and 10° field of view data for calculation, while using CIELAB color difference formula: ΔEab=[(ΔL)2+(Δa)2 +(Δb)2]1/2 to calculate the standard color The color difference between the sample and the color matching sample.
We can see that using computer color matching with the tristimulus value can make the color of the color sample to be matched with a specific light source expressed by data. There is a corresponding relationship between the tristimulus value of the color sample and the ink ratio, and the color difference can be used. Check to see if the recipe meets the requirements.
(3) Three stimulus color matching methods
The tristimulus value of each color patch of the chromatogram and the percentage of dots of each ink were input into the computer to establish a basic database. In color matching, the tristimulus value of the target color sample is input into the system, the system calculates the mixed ink and its proportion, and outputs the formula prediction result. When the ink color matching result is dry, the tristimulus value is measured again, and the computer calculates the difference in color according to the color difference formula, and further correction instructions are made to promptly formulate the high-quality homochromatic color.
In terms of the quality requirements of color reproduction, according to the national standards for the clear requirements of the color difference ΔE*ab of the same batch of color decorating prints, this paper selects ΔE*ab≤3.
Chromatography includes most of the common colors. For the colors in the chromatogram, you can directly find the ratio of the ink, not the color in the chromatogram. You can first find the color with the smallest color difference in the chromatogram, and then use linear interpolation. Solution.
3. Computer color matching system
(1) Function of color matching system
The computer color matching system is a modern device that integrates a colorimeter, a computer, and a color matching software system. The basic role of computer color matching is to pre-store the color data of the ink used in color matching in a computer, and then calculate the mixing ratio of the color of the sample draft with these inks in order to achieve the purpose of the predetermined formula.
(2) The composition of the color matching system
1 hardware part of computer color matching system
Computer: Use Windows operating system, hard disk storage space at least 20MB; Spectrodensitometer; Chromatography.
2 computer color matching software system
The software main menu: displays the program directories in the color matching system software, so that the operator has a general understanding of the color matching software, so that the operator selects and invokes the programs displayed in the directory according to his own purpose.
Basic data files: Use Microsoft's Access to create database files, including two-color overprinting, three-color overprinting, and spot color overprinting. The document includes the establishment, management, data processing part and recipe storage program of the basic data file.
3 Formula calculation and correction
Call this program to calculate the color difference between the color match sample and the standard sample, select the recipe based on the color difference, and correct the recipe.
The color matching system software has a strong human-machine dialogue function. The operator can input the corresponding parameters and data according to the prompt on the computer screen to obtain the required ink formulation.
Color matching is a complex technical project involving light color theory, ink, paper, process, etc. The use of chromatography to perform tristimulus color matching overcomes the limitations of KM theory and is suitable for the characteristics of the printing industry, reducing the burden on the color matching staff. , Improve the color quality of the product, color matching speed, accuracy, and increase economic efficiency. Although there are still many places to be improved, such as different color differences calculated by the tristimulus value matching under different light sources, the color matching accuracy has a great relationship with the accuracy of the chromatogram. However, with the constant updating of computers, the more sophisticated instruments, the constant emergence of various mathematical methods, and the gradual standardization and dataization of materials, computer color matching will inevitably show unparalleled superiority.
Source: "Printing Technology"
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